bevel shader not appearing in 2.79 on Mac
Cycles Bevel Shader is an experimental feature introduced after the release of Blender 2.79.

It is available in experimental trunk builds post release but not in official ones.

It is to be introduced to general public as a new Blender 2.8 feature as stated in the release notes.

It should also be used sparingly since it is computationally heavy and resource hungry. In most cases it is preferable to use geometry based solutions since it is cheaper to render then the shader, unless you encounter issues or glitches with complex geometry.